As you might know already – I seriously love rock climbing. And many other scientists that come to Antarctica share this passion. But a dead-flat ice shelf is probably the worst place to be a climber… so how do we keep up our strength in Antarctica?
Well, you have to be creative because there is no branch to do your pull up workout. Luckily Bruce and I had a fantastic idea and recycled our snow pit that was used for firn density measurements. Within our little rock climbing gym, we work not only on our pull up strength. But we also refran from building stairs out of it. So how do we get out of the snow pit? Hopefully with a muscle up by the end of the field work… and if not, we are probably still stuck in a snow pit.
What is the coolest thing in Antarctica? Hot-water drilling ! Because once the hole is finished, there is time to celebrate with style. But let me tell you more about it.
Bruce and I share a common love for digging in the snow. But even the keenest of snow diggers won’t get much deeper than a couple of meters below the surface. How can we get even deeper and all the way through the hundreds of meters of ice beneath our feet ?
We use hot water to drill a hole through the floating ice to gain access to the ocean underneath. Once the hole is finished we drop a sediment corer down through the hole, and pull an approximately 1.5 m long sediment core from the ocean floor. The core tells us when exactly the grounding line has retreated at this location – because sediments floating in the ocean waters can only settle if there is no ice. After we have pulled the core, we use two cameras that look up and downwards to film layers within our borehole and especially how the underside of the ice shelf looks like. Are there any rocks frozen into the ice (upward looking camera)? Or are there flourishing ecosystems on the ocean floor as described by Jules Verne’s science-fiction novel ‘10000 leagues under the sea’ (downward looking camera)? In our final step, we then deploy oceanic instruments through the hole to measure water temperature/salinity and the strength of the current. Additionally a series of thermistors are placed into the hole – all while racing against the time until the hole freezes again. So how long does it take to drill a hole?
Martin and Dale as the drilling specialists in our team say “it takes us about 2 days to prepare the drill, then 1 day to melt the snow for the drilling water, and once we have started drilling about 5 hours for a 400 m deep hole.” But then there is the magic moment when they melt their way through the last inch of ice and the hot water in the borehole escapes into the ocean cavity underneath. “We then have about 24 hours to do all the experiments before the hole freezes again.” I’m impressed, this means that they don’t get any proper sleep in several days ! Absolute heroes… So what do you do after everything is finished? “Well, there is still a lot of hot water left in our tanks – so we soak in the hot tub and enjoy the view.” I seriously can’t think of anything cooler than sitting in a hot tub on a glacier in Antarctica !
Today we explore the unknown lands of Antarctica. While we can map Antarctica’s surface with satellites, our knowledge of what lies beneath the ice is very limited. Radar can be used to estimate what Antarctica’s bedrock looks like and has revealed surprising results. For example, the South Pole’s surface elevation is 2835 m (9333 ft) and it sits on about 3000 m of ice. This means, that the weight of the overlaying ice is pushing the bedrock below sea level. So let’s cut a transect through Antarctica and have a closer look!
Our transect starts far away in the open ocean. Here, research vessels have been used in the past to map the ocean floor with sonar. These measurements show that the deep seabed goes down to below -4000 m beneath the ocean surface. As our transect reaches West Antarctica’s continental shelf, the ocean floor jumps up rapidly to -500 m and remains at this depth until we reach the West Antarctic Ice Sheet. The ice itself is heavy, and pushes the ocean floor back down. It is here where the ice is getting thicker towards the South Pole and the bedrock is sloping inland causing the West Antarctic Ice Sheet to be inherently unstable. Closer to the South Pole, the Transantarctic Mountains cause the bedrock to rise again which acts stabilizing. So where is the problem?
It is the areas where we can’t map the ocean floor from research vessels or airborne radar. This is because sea ice prevents ships to access certain areas, or because the ocean surface is covered by a 400 m thick floating ice shelf as for our two field sites. In these areas, active seismics is the only way to accurately map the ocean floor and pinpoint canyons in the continental shelf that allow warm ocean waters to access the West Antarctic Ice Sheet and cause rapid melting. What is active seismics? Now this will blow your mind – it means to use dynamite on the ice-shelves surface.
The seismic signals of the explosion travel through the ice shelf, are then reflected by the ice base and can be captured again at the surface. But some of the seismic signal even travels through the ocean waters underneath the ice, are then reflected by the ocean floor and captured by the same geophones on the surface. Atsu, as our seismologist, is then using these measurements to map the ocean floor underneath the ice shelf.
These maps then help us to answer fundamental questions of ocean circulation in this critical region. When did the ice thin to a point that our Dotson Camp site became ungrounded? This thinning would have made Bear Peninsula to a Bear Island, which allowed warm ocean waters to access parts of the ice shelf that is wasn’t able to erode before. Today we have made our first successful seismic experiment, and we are about to find out when!
Today we say goodbye to Cavity Camp on the Thwaites Glacier and move onto the Dotson Ice Shelf. We are very interested in this particular area, because several ‘ice rises’ have here become ungrounded in the last decade. Ice rises are high points in the ocean floor (like underwater mountains) on which the ice can rest. The additional drag from resting on these pinning points provides additional stability to the feeder glaciers (good). However, our satellite measurements show that all ice rises on the Dotson Ice Shelf become smaller and some have even detached already (bad). This is evident in the map, where grounding line rings from the early 1990s (blue) have become smaller over the millennium (yellow lines) and almost disappeared in 2014 (red). So why have they detached?
The reason is most likely, that the ice has thinned so much from basal melting, that it is not thick enough anymore to rest on the tops of the underwater mountains. Our measurements will (a) show that this is the explanation for the disappearance of pinning points, and (b) highlight areas of rapid basal melt. So how do we measure basal melt in the field from the surface of the ice shelf?
With an Auto-phase sensitive radio echo sounder (or short, the ApRES). This state-of-the-art instrument has been developed by the British Antarctic Survey and is our Starship Enterprise in the fleet of glaciological instruments. What makes it so special? The instrument can measure ice thickness at its location to millimeter accuracy. This means that if we take a measurement and return after one week, we can measure the change in ice thickness at this location. But here is an example:
Let’s say we take a measurement today (light blue curve in the graph) and the depth of the ice base below the surface is 650.42 m. We then return after one week and take the measurement again on exactly the same location and it is 650.0 m (yellow curve). This means that 42 centimeters will have melted away in 7 days at this location – this corresponds to a rate of 25 m (82 ft) per year ! Holy penguin.
But the scientist in you says that 7 days isn’t long enough to represent an entire year, right? For this reason we first measure as many of these points as possible (light blue circles in the map) and then repeat them after 7 days. We can now tell the areas with high from the areas with low basal melt. We then modify the ApRES from attended mode to unattended mode and leave the instrument sitting in the field – continuously transmitting its measurements via satellite link to my warm office in Oregon. With this time series we can now tell if our map of basal melt rates from the repeat measurements is representative, or if there are seasonal trends of increased basal melting. I’m particularly interested if the basal melt is connected to ocean tides which might play an important role in this crucial area.
phote courtesy of Daniel Price
What lies beneath our feet? Measuring the ice thickness and quantifying the amount of accumulation is essential for glaciological research. But how do we do that? A common method consists of pulling a radar behind a skidoo on the ice surface or hauling the system by foot.
Ground penetrating radar (GPR) is a useful tool for mapping of features hidden under the ice surface. As ice is very transparent to radar signals, the signal can penetrate deep from the transmitting antenna into floating glaciers and ice shelves. Layers within the ice then act like a mirror and reflect parts of the signal back to the receiving antenna on the surface. We then record how much time it took between sending it out and receiving the signal – the so-called ‘two-way travel time’. From the lab we know how quickly radar signals travel through ice, so we can easily convert the two-way travel time directly to depth of the reflecting layer below the surface. But here is an example:
From the gym we know that Usain Bolt travels with 10.44 meters per second through air. If we let him race for 4022 s, he would have run 42 kilometers (that’s a marathon in 67 minutes). And now you say that he will get tired and can’t keep his 10.44 m/s up for that long. So how long can he keep it up? His world record over 200 m is 19.19 seconds – that is only 2.003 times his time over 100 m. So he can keep it up for at least 200 meters ! Anyway, you get the point. If you know the travel velocity of Usain (or radar) through a medum (like ice) and you stop the time, you can calculate the overall distance. But there is one mistake that can happen even to the best radar-glaciologist… the measured ice is suddenly twice a thick as expected, why ? Because you still have to divide the two-way travel time by a factor of 2.
But as easy as it sounds, there is a bit more to it. Different radar waves can penetrate to different depths – with lower frequencies penetrating ice thicknesses up to several kilometers. With these low-frequency radar systems we can then see what lies beneath the ice. Is it grounded on bedrock or floating on the ocean? Are there basal channels at the ice base through which meltwater is discharged? Or are there any crevasses at the bottom of the ice? Higher frequency radar systems don’t penetrate all the way to the ice base as their signals are reflected from internal layers near the surface. With these systems we can measure how thick eventual snow bridges are over burried crevasses or if there are any spatial differences in snow accumulation. Sometimes we see very clear internal layers and need to have an even closer look. We can then either drill an icecore to retrieve a sample, or if it is closer to the surface we do it the old way and grab a shovel and start digging. If there is one thing I have learned in Antarctica, it is digging.
Unfortunately though, radar isn’t perfect… as useful as it is for measuring internal layers and ice thickness, radar doesn’t tell us anything about the ocean floor underneath. Other techniques, such as (a) gravimetry measuring spatial differences of the strength of the gravitational field, and (b) active seismology using seismic waves from controlled explosions, can be used to map the ocean floor.
After snowfall bound us to our tents for the last three days, clear blue skies and crisp conditions allowed the first field measurements on the Thwaites Glacier today. The ice is generally thinner than we have estimated from satellite data before coming to Antarctica. This is important because it indicates a change in the structural stability of this part of Thwaites Glacier. Underneath our camp, ice thickness is just about 300m, followed by 550m of ocean water to the sea floor.
Due to the good flight conditions this evening we were also visited by a BBC crew. They are filming a new documentary about climate change in Antarctica and were really impressed by our beautiful Cavity Camp. As this is a collaboration between the US and the UK, we offered our new English friends a warm cup of tea – with water freshly melted from snow, and full cream milk powder to add these extra calories to keep them warm.
We are all very much looking forward to a busy time over the holidays as the weather forecast for Antarctica promises a White Christmas… Hohoho
Stay cool everyone,
Hello World from the Thwaites Glacier. We, the TARSAN team, have made it to our first study site in the Amundsen Sea. We have now established Cavity Camp and will finally start to acquire field measurements in the coming days.
Martin and Dale get their equipment ready to start drilling through the 400 meters of ice underneath our feet. They will stay close to our camp site together with Bruce, Ted and Doug who assemble the instruments that will go later down into the borehole. Blair and Cece will recce our travel routes and make sure that we only operate in safe terrain. Atsu and Karen head out for some seismic experiments. Erin and I will first focus on point measurements of ice thickness and later acquire radar profiles of ice thickness across the Thwaites Glacier. Let’s all cross our fingers (and flippers) that the weather cooperates and we get the job done bananas (or sardines).
“Hello party people! This is Dr. Wild speaking. Welcome aboard Venga Airways. After take off we’ll pump up the sound system ‘Cause we’re going to WAIS Divide!”
Today we leave the comfort of McMurdo Station behind us (we have been here for 1 month already) and finally depart to WAIS Divide – an intermediate camp before we reach our deep field sites on the Thwaites Glacier and Dotson Ice Shelf. We step onto a C-130 plane, aka Hercules, and fly across the Ross Ice Shelf which has about the size of France. On our way, we pass the Siple Coast, and land on the West Antarctic Ice Sheet Divide. As the name suggests, the ice flows in two different directions from here. One part flows towards the Ross Ice Shelf, the other drains through the Thwaites Glacier and into the Amundsen Sea. This ice divide is an important boundary and the place where kilometer long ice cores were drilled in the past…
Along our journey, we first enjoy the spectacular views of the Transantarctic Mountains until we pull into the endless white of West Antarctica. The flight on a C-130 is very entertaining; loud noises of the engines, flashing lights, dripping water, and people staring at each other throughout the flight. Passengers sit along the sides of the aircraft, while the central area is reserved for cargo. The flight attendants are soldiers from the US Air Force, and the in-flight entertainment consists of a visit to the aircraft’s cockpit. Yes, there is a toilet – but it is a bucket behind a curtain in the back of the plane. You don’t want to spend much time here anyway, as it is getting colder towards the back. After about 3 hours on the plane, we land on the ice runway next to WAIS Divide camp.
The camp itself is only open during the austral summer months. There is a galley in the central area, neighbouring tents for science and lots and lots of cargo standing around. We sleep in ‘tent city’ which is a bit away from the rush of the runway. According to the plan, we will enjoy some privacy at WAIS Divide and sleep in individual mountain tents. On the Thwaites Glacier and on the Dotson Ice Shelf we will mostly sleep in Scott Polar tents in pairs of two… unless we build an igloo…
This is how to Build an Igloo : Check
There is a lot to discover in Antarctica – lakes underneath the ice sheets, meteorites on their surface, or historic artifacts from the polar heroes. And while I would love to tell you all about these, today we discover something completely different… urban treasures ! When walking around McMurdo Station, I have noticed a lot of artwork which reminded me of past experiences on the ice.
While being a tutor for PCAS in the 2017/18 Antarctic season, I was chasing wildlife with the students around the clock. Seals, penguins and skuas were very exciting in the beginning, but we quickly realized that this was our once in a life-time chance to see whales in Antarctica. For this reason we spent long nights on whale watch overlooking the open waters near McMurdo. Our patience was finally rewarded… not only with breathtaking views during the midnight sun, but also with Minke and Killer whales right in front of us. I like to think back to my PCAS experience, where I shared many once in a life-time moments with an amazing group of humans.
During my first deployment to Antarctica in the 2014/15 season, my friend Dan Price and I spent almost an entire day walking side-by-side along the ice. We were measuring snow accumulation and had to probe snow depth and dig many snow pits on our way across the ice shelf’s grounding line. In the end, we have moved around 5 cubic meters of snow that day and probed 100 times its depth, but we have learned that accumulation is about three times higher near the grounding line than it is on the floating ice shelf – one result of my PhD thesis that I would finish almost 5 years later.
In the same season, we were travelling back to Scott Base using 3 skidoos and a sledge. Just a couple of kilometers before we would return after almost one month on the ice, one of our skidoos broke down. And because of this delay we missed the fish’n chips dinner that we were craving at this point. Unable to repair our skidoo, it is now exhibited in the Antarctic center in Christchurch where you we can still see it today.
And then there is the troll hiding under the bridge. I have been crossing this bridge for weeks on my way between the Crary science labs and the galley at McMurdo. Life at Station is monotone, with the same daily routine for a very long time. And as I was crossing the bridge one fine morning, still sunk into deep thoughts, the troll suddenly caught my eye – I immediately had to laugh out loud. Today, I double-check every single time when I cross the bridge if the troll is still there.
Thanks artists of McMurdo – you brighten up this place more than the midnight sun.
Antarctica is the most hostile environment on the Earth and safety is our number one priority when working on the ice. The danger of hypothermia, frostbite and crevasses are obvious – a scientific measurement is not worth to risk our lives and jump over a crevasse ! But how do we minimize these risks in practise ?
The Antarctic Field Training is mandatory for everyone who comes to Ross Island. It’s a thorough education in the use of our survival equipment and only the beginning of a proper risk assessment. Lessons like Extreme Cold Weather clothing, Skidoo and generator repairs, usage of cooking stoves as well as pully-systems for crevasse fall rescue are practised indoors at first. But it is during the ‘Shakedown’ when we camp out on the ice near McMurdo Station and practice these skills outdoors. With such an experienced team like ours, lot’s of tips and tricks are constantly exchanged between us. For example, always bring a small shovel into your tent in case you get snowed in over night and you have to dig your way back out in the morning. Or wear your lipstick on a chord around your neck to avoid losing it in the large number of pockets in your clothes. But there is so much more that we can do before heading to the field to minimize the risk of injury.
Satellites regularly observe what happens on Antarctica’s ever changing surface. Some of them take pictures like your phone that show us opening surface crevasses from a bird’s eye perspective. But what if a crevasse is hidden beneath a thin layer of snow and not visible on the surface ? Radar satellites send out a signal that penetrates into the snow and shows us how thick snow bridges across these crevasses are. If we detect any crevasses in the radar images, we then draw them onto a map and exclude these areas from our travel routes.
So if we can see into the snow with satellites, why do we have to go to Antarctica in the first place ? It is because these radar satellites are so high up in the sky ! They will never send out a signal that is strong enough to go all the way through the ice and see what is going on beneath the ice. For this reason we travel to areas in Antarctica which show the most rapid changes on the surface. We then bring scientific instruments that are strong enough to penetrate all the way to the ice base and beyond, such as Ground Penetrating Radar or active seismics.
We then measure with these instruments in areas that we consider crevasse free from our satellite data analysis (the green areas in the two maps above). Within these areas, we still travel with linked skidoos or even roped up on skis to minimize any remaining risk. And in the case somebody would still fall into a crevasse, we practise crevasse rescue first indoors and later on a safe practise crevasse near McMurdo.